The invention relates to a new and improved process for the preparation of [2,2]-paracyclophane (I).
I is a known substance which can be used as an intermediate, inter alia, for the preparation of poly-p-xylylene, which is useful for coating electronic components and assemblies and other precision parts.
Several processes have been described for the preparation of I, but these have considerable disadvantages for industrial production.
Thus, Hofmann elimination, from p-methylbenzyltrimethylammonium hydroxide (II) in the presence of a base (compare Organic Syntheses, Coll. Vol. 5, John Wiley & Sons, Inc., New York/London/Sydney/Toronto, 1973, pages 883-886; Thesis R. Nader, Univ. Gottingen, 1978, page 89) and pyrolysis of p-xylene with water vapor at about 900.degree. C., each give only low yields (maxima of 17-19% reported); in addition, undesired polymeric products are produced to a greater or lesser extent (up to 80%).
In the 1,6-elimination of (p-trimethylsilylmethylbenzyl)trimethylammonium iodide with tetrabutylammonium fluoride (compare J. Org. Chem., Volume 46, 1981, pages 1043-1044) the yield is in fact higher (56%), but the starting materials are not readily accessible and are costly, so that this process is not suitable for industrial preparation.